It has been the research hotspot and difficulty in the photovoltaic field to use cheap materials for preparation of the solar cell having low cost and high efficiency. The current silicon solar cell used for ground has complicated production process and high cost, making its application restricted. In order to reduce the cost and expand the scope of application, people have been looking for a new solar cell material for a long time. The polymer solar cell has attracted a lot of attention because of such advantages as low-priced raw materials, light weight, flexibility, simple production processes, and allowance of preparation of large area by coating, printing and other means. It will have a very huge market prospect if its energy conversion efficiency can be improved to near the level of the commercial silicon solar cell. Since N. S. Sariciftci et al. reported in 1992 in the SCIENCE (N. S Sariciftci, L. Smilowitz, A. J. Heeger, et al. Science, 1992, 258, 1474) about the photoinduced electron transfer phenomenon between the conjugated polymer and C60, the polymer solar cell has received a great deal of research and obtained rapid development. Currently, the research of the polymer solar cell is mainly focused on the blend system of the donor and acceptor; the energy conversion efficiency of the blend system of PTB7 and PC71BM has attained 7.4% (Y. Liang et al., Adv. Mater.; DOI:10.1002/adma.200903528), but is still much lower than that of the inorganic solar cell. There are the following main limiting factors that restrict the performance improvement: The organic semiconductor device has a relatively low carrier mobility, the device has a spectral response not matching with the solar radiation spectrum, the red light region having a high photon flux has not been used effectively, and the carrier has a low electrode collecting efficiency, etc. In order to make the polymer solar cell get actual application, it is still the priority of the research area to develop new materials and greatly improve the energy conversion efficiency.
Perylenetetracarboxylic diimide and its derivatives have a large co-benzene-ring plane structure and a two-imine-ring structure, strong absorption in the visible light region, high light, heat and environmental stability, high electron affinity (a low LUMO level), and high electron mobility along the stacking direction because of the π-π stacking between its big conjugated π bonds. Therefore, it has shown broad application prospects in a variety of fields such as the organic solar cell. However, because perylenetetracarboxylic diimide and its derivatives contain a large planar conjugated system as well as have good molecular coplanarity, strong interaction of the intermolecular big π bond, and high lattice energy, they have poor solubility and film-forming processing performance, which make the prepared device prone to the phase separation problems, thus affecting the exciton diffusion efficiency and leading to the loss of energy. Besides, perylenetetracarboxylic diimide and its derivatives, having absorption spectra mainly concentrated in the visible region, have an absorption range not wide enough and a degree of matching with the sunlight emission spectrum not high enough, and thus cannot effectively use the sunlight, which also reduces the photoelectric conversion efficiency of the organic solar cell.